Morphology of negatively stained VSV at pH 7.5, 6.0, and 5.5. (A) At pH 7.5, VSV formed a monodisperse suspension with virions that were bullet shaped when viewed from the side and circular when viewed from above. The asterisks indicate viruses with a base depleted of glycoproteins. (B) Higher magnification of the virions indicated by an arrow in A. Continuous layer of G over the surface of the virus (large arrow), with a lower density at the base of the particle (thin arrows). The right arrow indicates a virus with no spikes visible at its base. (C) VSV forms large aggregates at pH 6.0. G has a more elongated structure, making it possible to distinguish individual spikes, which are often closely packed at the apex of the viral particle (arrows). (D) At pH 5.5, the spikes form ordered helical arrays. Note that the viral particles fuse at their bases. The nucleocapsid is now clearly visible, indicating that the stain penetrated the viral particle.